What are the appropriate dosing, monitoring, and contraindications for initiating flecainide in an adult with symptomatic supraventricular tachycardia and no structural heart disease?

Flecainide for Symptomatic Supraventricular Tachycardia

Flecainide is a reasonable second-line option for adults with symptomatic SVT who have no structural or ischemic heart disease, starting at 50 mg twice daily and increasing by 50 mg every 4 days up to a maximum of 300 mg/day, with mandatory co-administration of a beta-blocker or non-dihydropyridine calcium channel blocker to prevent 1:1 AV conduction if atrial flutter develops. 1, 2

Absolute Prerequisites Before Initiation

Before prescribing flecainide, you must confirm:

• No structural heart disease on echocardiography—this includes any significant ventricular dysfunction, left ventricular hypertrophy >1.4 cm, hemodynamically significant valvular disease, or NYHA Class III-IV heart failure 1, 3
• No ischemic heart disease—coronary artery disease of any severity is an absolute contraindication per European Society of Cardiology guidelines 3
• Normal baseline ECG—no sinus or AV node dysfunction, bundle branch block, QT prolongation, or Brugada pattern 3
• Normal renal function—if creatinine clearance ≤35 mL/min/1.73 m², start at 50 mg once daily with frequent plasma level monitoring 2

Dosing Algorithm

Initial Dosing

• Start at 50 mg every 12 hours for PSVT and paroxysmal atrial fibrillation 2
• Increase by 50 mg twice daily every 4 days until efficacy is achieved 2
• Maximum dose is 300 mg/day (150 mg twice daily) for supraventricular arrhythmias 2
• Steady-state plasma levels require 3-5 days at each dose due to the 12-27 hour half-life 2

Efficacy Expectations

• Flecainide renders sustained tachycardia non-inducible in 85% of patients with AVRT 1
• Only 24% recurrence rate versus 85% on placebo in controlled trials 1
• When combined with beta-blockers, efficacy increases to >90% for abolition of symptomatic tachycardia 1
• Long-term follow-up shows 87% of patients remain symptom-free over 3.9 years 4

Mandatory Co-Administration of AV Nodal Blockers

This is critical to prevent life-threatening 1:1 AV conduction:

• Administer a beta-blocker or non-dihydropyridine calcium channel blocker (diltiazem or verapamil) at least 30 minutes before the flecainide dose 3
• Continue the AV nodal blocker as background therapy throughout the entire course of flecainide treatment 3
• Without AV nodal blockade, flecainide can convert atrial fibrillation into atrial flutter with rapid 1:1 ventricular conduction, causing hemodynamic compromise 3

Monitoring Requirements

First 14 Days (High-Risk Period)

• Obtain baseline 12-lead ECG and measure QRS duration 1, 3
• Monitor for proarrhythmia, especially during the first 2 weeks 1
• Immediately discontinue if QRS duration increases >25% from baseline or exceeds 150% of baseline—this indicates dangerous sodium channel blockade 3

Ongoing Monitoring

• Repeat ECG at steady state (after at least 5 doses or any dose change) 2
• Therapeutic plasma levels are 200-500 ng/mL; levels >800 ng/mL may be required in some cases but increase risk 2
• In patients with renal impairment, frequent plasma level monitoring is mandatory 2

Common Pitfalls to Avoid

• Assuming "mild" structural disease is safe—the decisive factor is hemodynamic significance (chamber enlargement, elevated pressures, ventricular dysfunction), not anatomic severity 3
• Failing to co-administer AV nodal blockers—this is the most dangerous error and can lead to rapid 1:1 flutter conduction 3
• Rapid dose escalation—increases in dosage more frequently than every 4 days increase the incidence of proarrhythmic events and CHF 2
• Using in patients with any coronary disease—even mild ischemic heart disease is an absolute contraindication based on CAST trial mortality data 1, 3

When Flecainide Fails or Is Contraindicated

If structural heart disease develops or flecainide is not tolerated:

• Amiodarone is the first-line alternative for patients with structural heart disease 3
• Dofetilide is another option but requires inpatient initiation 3
• Sotalol may be used but requires inpatient initiation with careful QT-interval monitoring 3
• Catheter ablation should be strongly considered as definitive therapy, with single-procedure success rates >90% for most SVTs 5

Guideline Positioning

The ACC/AHA/HRS 2015 guidelines give flecainide a Class IIa recommendation (reasonable option) as second-line therapy for AVNRT/AVRT, only after:

• First-line agents (beta-blockers, diltiazem, or verapamil) are ineffective or contraindicated 1
• The patient is not a candidate for or refuses catheter ablation 1
• All contraindications have been excluded 5